Electromagnet uncoupler

[Aikidomaster]

I read an article in one of Model Railroaders supplemental books about railroad yards. In it, they suggested the use of Kadee #309 electromagnetic uncouplers on the mainline and passing sidings and regular magnets under the track for sidings. As a "4F" electrical engineer, it is with some fear and trepidation that I contemplate the use of electromagnets. I have purchase a couple of them and am trying to wire them. My father-in-law bought a circuit board to place the rectifer and capacitor. I am using an 18 volt AC power source. Need help with the circuit board wiring. Craig

[nedthomas]

The # 309 will work on 16-18 volts AC or DC. Use a good quality pushbutton as the uncoupler will burn up if left engerized too long (shorted button). The unit draws 3 amps so a 3 amp transformer or higher is required. Using a rectifer and capacitor will raise the voltage to about 24 volts DC.

[larak]

Probably best to use a DC supply with a "reverse biased" (normally open) diode across the pushbutton to prevent the back emf spike from arcing across the switch.

nedthomas

the uncoupler will burn up if left engerized too long (shorted button)

 

Sounds like a good candidate for a capacitor discharge power supply.

Karl

[rrinker]

larak

Probably best to use a DC supply with a "reverse biased" (normally open) diode across the pushbutton to prevent the back emf spike from arcing across the switch.

nedthomas

the uncoupler will burn up if left engerized too long (shorted button)

 

Sounds like a good candidate for a capacitor discharge power supply.

Karl

 You need a pretty hefty diode to handle the 3+ amps. A common 1N4001 type won;t handle it.

And a CD power supply will result in too short a pulse to be able to uncouple and set the delayed action - the magnet has to be active that whole time.

I really don't liek the Kadee electromagnet for that reason, it draws WAY too much power relative to other railroad things these days. If your locos run smooth and you cars are all free rolling, they won't uncouple accidently while running through on the main. It also helps a lot if you use ONLY Kadee couplers - I replace any if cars and locos that aren't with the genuine article because they just work better. Another way to uncouple withotu any magnets is to use a bamboo skewer - 100 for a buck at the dollar store. Sand or file a flat at the pointy end, you stick it in the knuckles and twist to open the coupler. Cheap, effective, guaranteed to only uncouple when you actually want to uncouple, and it puts you in the position of the brakeman pulling the pin.

                                                     --Randy

 

[larak]

rrinker

 You need a pretty hefty diode to handle the 3+ amps. A common 1N4001 type won;t handle it.

 

 Like these?

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=36273

Used to be VERY common in the TV service industry (in the days where we actually repaired them). Under 10 cents a piece too.

rrinker

And a CD power supply will result in too short a pulse to be able to uncouple and set the delayed action - the magnet has to be active that whole time.

 

Probably, although I'd like to see the curves. Properly sized cap (tune it to the inductance using a bit of calculus perhaps) with a small series resistor might do it.  Personally, I use rare earth magnets for most uncoupling and make my own electro-magnets. I don't like the kaydees either.

Karl 

[nedthomas]

Another option is to use the #308 under the track uncoupler. Install it on a hinge so it will hang down at 90 degrees to the roadbed. Use string, fishline or choke cable to move it into position under the track when in use.  MR has run some articles on this in the pass. This requires the sub-roadbed be cut out so the upcoupler can be moved into position just under the ties.

[MisterBeasley]

I found a 12-volt, 1 amp wall wart that I use for the uncoupler.  It's not used for lights, turnouts or anything else like that.  When I had it hooked up to my lighting circuit, the whole town would experience a brown-out when I pushed the button.  These things do use a lot of power, so it's best to have them completely isolated from the rest of your layout wiring.

I made the big mistake of installing the uncoupler after I'd glued and ballasted the track, over 2 inches of foam.  It was an exercise in poor planning that taught me a lesson.

I'd agree on not using a CD circuit.  I practice, I need the uncoupler to be active for several seconds, particularly if I'm setting a delayed uncoupling.

[rrinker]

 I'm really surprised you got it to work with a 1 amp wall-wart, without blowing the wall-wart. I got one Kadee electromagnet to test, and hooked it to the AC terminals of an old MRC power pack I had and basically all that happened was the breaker tripped int he pack after a couple of seconds, and it never really had much magnetic strength. Wall-warts are typically overload protected with a non-replaceable fusible link - exceed the current rating and the link opens like a fuse to prevent meltdowns and/or fires, and at that point - time to toss the wall-wart. That's why you have ot be careful about shorting them out when runnign wires for structure lights or whatever else you are using them for,

                                           --Randy